I will brew an Irish Red next week and plan to let it in the primary at 66F for two weeks (or until FG is almost reached) than transfer it to secondary and let it cold condition for 4 weeks at 40F. The goal is to clear it up and have the smoothest Irish Red possible.

My worry is about the yeast left after this cold conditionning. I will use WLP004 Irish Stout, so it ain't a lager strain.

Should I add another pack of yeast at bottling or there will be eough left ?

I always make a 1,5L starter with 2 packs of yeast with yeast nutrient and constant aeration before pitching.

Would a little pack of dry yeast do the job ? Isn't it risky for contamination ?

I believe that if you add 1/2 of a dry yeast pack Fermentis 05 for instance it should be enough. Make sure you re-hydrate the yeast then dump it into your fermenter, stir it slowly then put the lock back on and wait 2 or 3 days then rack to your bottling bucket and prime and bottle. This will insure that you will have ample fresh yeast for carbonation....Oh also, before pitching the yeast, bring the temp of the beer back up to 68 - 70 degF...this will not stress the yeast out and will keep the little guys comfy and ready for their final job!

I've never done what you propose, but think I can provide a somewhat educated opinion. Since you are using ale yeast and plan to chill the secondary down to 40F -- for FOUR weeks, no less -- I would bet my next paycheck that virtually all of your yeast will have completely flocculated out. If, by some miracle, you actually have a few yeasties floating around in your cold beer after that long, I am confident that they will be far too few to carbonate your bottles within any reasonable length of time. Now, you might think that it doesn't matter if it takes three or four times as long to carbonate -- if it EVER does -- but I think it is better for the beer to carbonate as soon as possible. This is because, despite using a bottling wand to minimize aeration, you at least have air space at the top of the bottle, and I want my yeast to help use that up as quick as possible, as well as get rid of any food that any bacteria could use; it would be virtually impossible to eliminate all bacteria during bottling no matter how sanitary you are. There is airborne bacteria, if nothing else. Now, I use oxygen absorbing caps, but I don't really trust them, and use them only because that's all that are available at my LHBS. I don't trust them because they sit around for how many months exposed to the atmosphere, and there must be a limit to how much oxygen they can absorb. To me, it's just a gimmick that I don't want to rely on, so I want my bottles pretty much carbonated within a week if possible, and they usually do. But I don't think that this would even be possible -- at all -- with your plans, unless you add fresh yeast.

I think wottaguy has given good advice. An alternative is what I have done in the past when I have had a beer sit for so long in the fermenter that I suspect I probably have a low suspended yeast count. In that case, I make it a point to plan to brew either on bottling day or the next day, and since I always make a starter, I just make some extra and pour that into my bottling bucket along with my primer. I then siphon my beer into the bottling bucket which helps mix it all, and also give it an occasional stir without aerating it. In your case, the only extra step you need is to move your fermenter from the refrigerator to someplace where it can thoroughly warm to room temp before you mix it with the starter and primer.